JP2004177823A

JP2004177823A - Liquid crystal display

Info

Publication number: JP2004177823A
Application number: JP2002346261A
Authority: JP
Inventors: Shin Tabata; 伸田畑; Takahiro Nishioka; 孝博西岡; Yasunori Niwano; 泰則庭野
Original assignee: Mitsubishi Electric Corp; Melco Display Technology Inc
Current assignee: Mitsubishi Electric Corp; Melco Display Technology Inc
Priority date: 2002-11-28
Filing date: 2002-11-28
Publication date: 2004-06-24

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid crystal display which prevents coloring of display due to highness of induced birefringence of a liquid crystal layer. <P>SOLUTION: The liquid crystal display is a semitransmission type liquid crystal display wherein liquid crystal alignment is parallel alignment. In a transmission type liquid crystal display element having a polarizing plate, a retardation film of nearly λ/2 to wavelength λ of light, a retardation film of nearly λ/4, and a glass substrate of a panel on the surface of the panel on the viewer side of the liquid crystal display from the viewer side, the slow phase axis of a phase difference compensation layer constituted by superposing the two retardation films on each other nearly coincides with the alignment direction of a liquid crystal and the induced birefringence value of the phase difference compensation layer is set to be lower than λ/4. <P>COPYRIGHT: (C)2004,JPO

Description

【０００１】
【発明の属する技術分野】
本発明は液晶表示装置に関する。さらに詳しくは液晶層の複屈折が大きくなったことによる表示の着色を防止することができる液晶表示装置に関する。
【０００２】
【従来の技術】
液晶表示装置は大きく反射型、透過型の２種に大別することができ、携帯電話用の表示装置のように、使用環境に応じて、その両者を必要とする場合、半透過型と呼ばれる表示素子構造が用いられている。この半透過型液晶表示素子の基本的な構造の概要は先行出願等に開示されている（特許文献１参照）。
【０００３】
特許文献１に示された先行出願によると、半透過型液晶表示素子は同一画素内に透過表示を行なう領域Ａ（図１参照）と反射表示を行なう領域Ｂ（図１参照）を有し、携帯電話用表示素子に用いた場合、通常の操作時には、表示素子の背面に設置したバックライトを点灯させ、液晶表示素子を透過してきたバックライトからの出射光による領域Ａの表示を観察し、待機時にはバックライトを消灯し、液晶表示素子内で反射した外光による領域Ｂの表示を観察するものである。したがって使用環境によらず良好な表示を行なうことができ、また消費電力も少なくすることができるため、携帯電話等の表示素子に適している。
【０００４】
特許文献１に示された半透過型液晶表示装置の構造例を図１に示す。液晶層２２、２３は基板２１ａ、２１ｂに狭持された構造をしており、観察者側（図の上方）に円偏光板１１を、背面側（図の下）に円偏光板１２を有しており、基板２１ａ上の透明電極３３および基板２１ｂ上の透明電極３３、導電性を有する反射鏡３１間に印加される電界による液晶層２２、２３の複屈折変化により表示を行なうことができる。
【０００５】
一般に液晶層２２と２３の厚さは異なって設定され、その違いは基板２１ｂ上の有機膜３２の厚さで調整することができる。その調整手法、作成手法は他の先行出願に詳しく、また本出願の目的ではないので省略する（特許文献２参照）。
【０００６】
つぎに図２の座標系を用いて各構成材料の光学的な機能等を説明する。図２において、Ｔ_１、Ｔ_２は透過軸方向、Ｌ_１、Ｌ_２、Ｌ_３、Ｌ_４は遅相軸方向、およびＲ_１、Ｒ_２はラビング軸方向である。
【０００７】
図２において、基板２１ａと２１ｂのラビング方向は一致しており、いわゆる平行配向（反平行配向を含む）と呼ばれる液晶の配向状態としている。両基板面上の電極に電界を印加すると、正の誘電異方性の液晶材料を用いている場合、液晶分子は、電界無印加時の基板面にほぼ平行な配向状態から徐々に基板面から立ち上がった配向へ変化し、それにともなって、複屈折性が減少する。もっとも基本的な構成の場合、電界無印加時の複屈折を、反射表示を行なう液晶層２２では光の波長λに対してλ／４、透過表示を行なう液晶層２３ではλ／２となるように液晶材料およびおのおのの液晶層の厚さを調整する。電界を印加し、液晶分子が基板面にほぼ垂直となったときには複屈折はほぼ０となるため、電圧印加による複屈折性の変化は、反射部でλ／４（反射部では入射光は往復するので、実質的にはλ／４×２＝λ／２）、透過部ではλ／２となる。実際には電圧印加時の複屈折は完全には０にはならないので、液晶層２２、２３の電圧無印加時の複屈折はやや大きめに設定することが多い。
【０００８】
位相差板２と位相差板３は２枚合わせて広い波長範囲でλ／４の特性を示すように配置するもので、一般的には位相差板２はほぼλ／２、位相差板３はλ／４の特性を有する一軸延伸フィルムを用いる。ただし近年、単独で用いても広い波長範囲でλ／４の特性を示すフィルムも開発されており、その場合、位相差板２は省略することが可能である。
【０００９】
位相差板５、６も２、３と同様に合わせてλ／４となるように配置されており、特性に応じて位相差板５は省略可能である。
【００１０】
以上より先行例に記載されている代表的な構造およびおのおのの部材の機能をまとめると以下のようになる。
偏光板１：入射、出射光を直線偏光に変換
位相差板２、３：合わせてλ／４
液晶層２２：複屈折λ／４（反射により往復するためλ／４×２＝λ／２）、電圧印加時ほぼ０
液晶層２３：複屈折λ／２、電圧印加時ほぼ０
位相差板５、６：合わせてλ／４
偏光板４：バックライトの光を直線偏光に変換
【００１１】
このとき表示のメカニズムは以下のようになる。
【００１２】
＜＜反射表示＞＞
（白表示：電圧無印加）
位相差板２，３は入射時λ／４、反射時λ／４で合計λ／２として寄与する。
【００１３】
液晶層は往復λ／２として寄与する。合計λになる。
【００１４】
したがって偏光板１を通った直線偏光は１周期位相がずれ、もとの偏光状態で偏光板１に戻ってくるため偏光板１を透過でき、白表示となる。
【００１５】
（黒表示：電圧印加により液晶層の複屈折＝ほぼ０）
前記と同じで位相差板は往復でλ／２として寄与する。
【００１６】
液晶層は０。合計λ／２になる。
【００１７】
偏光板１を通った直線偏光は、１／２周期位相がずれるため、もとの偏光状態から９０°回転して偏光板１に戻ってくるため偏光板１を透過できず、黒表示となる。
【００１８】
＜＜透過表示＞＞
（白表示：電圧無印加）
位相差板２、３と５、６でλ／４×２＝λ／２になる。
【００１９】
液晶層はλ／２になる。合計λになる。
【００２０】
偏光板４を透過した直線偏光は、同じ偏光状態で偏光板１に到達するため、偏光板１と４の透過軸をほぼ一致させておけば白表示となる。
【００２１】
（黒表示：電圧印加により液晶層の複屈折＝ほぼ０）
位相差板は合計λ／２になる。
【００２２】
液晶層は０。合計λ／２になる。
【００２３】
偏光板４を透過した直線偏光は、９０°回転して偏光板１に到達するため、偏光板１と４の透過軸をほぼ一致させておけば透過することができず黒表示となる。
【００２４】
【特許文献１】
特開２０００−１８７２２０号公報
【特許文献２】
特開平１０−１８６３５９号公報
【００２５】
【発明が解決しようとする課題】
現在使用可能な液晶材料の屈折率異方性（Δｎ）は波長５５０ｎｍに対して０．０６５〜０．１であり、これらの液晶を用いて反射部分で複屈折（Δｎｄ：ｄは液晶層厚）をλ／４とするためには、２．１ミクロン以下のパネルギャップとしなければならないが、現状のパネル製造プロセスでは２．５ミクロンが安定して作成できる下限である。したがって反射部分の液晶層の複屈折が大きくなってしまい、まず第１の問題として着色が大きくなる。一般にこのような場合、黄色い着色が顕著となり、表示品位を著しく低下させると言う問題がある。
【００２６】
また本出願の液晶表示装置では、液晶層の液晶配向を平行配向のみについて記載しているが、従来は液晶配向をねじれ配向（上下基板間で液晶の配向方向が異なり、上下基板のあいだで液晶分子がねじれた配向をしている）とした半透過型液晶表示素子も多く開発されていた。このねじれ配向を用いた場合、反射部分に関しては先に説明したメカニズムと同様に白黒の表示を行なうことができるが、透過部分に関しては白表示時に、上偏光板に到達したとき楕円偏光となり、その１偏光成分しか透過できないので光の利用効率が本件の平行配向としたときに比べ１／２となると言う問題があり、平行配向を用いることで大きな改善をすることができたという経緯がある。
【００２７】
先に示した着色の問題を解決するために、液晶層の観察者側の偏光板、位相差板を調整すると、多くの場合、せっかく平行配向を採用したことによって得られた、透過部分での高い透過率を犠牲にすることになる。
【００２８】
そこで本発明では、平行配向を用いた高い透過率を充分に維持しながら、反射部分の着色を低減するパネル構成を提案する。
【００２９】
【課題を解決するための手段】
液晶表示素子の観察者側の位相差板３または位相差板２と３を合わせて形成される位相差層の遅相軸を液晶の配向方向とほぼ一致させ、さらに複屈折値を光の波長λに対してλ／４より小さくする。複屈折値をλ／４より小さくする程度は、反射部の液晶層の複屈折値がλ／４を超えた量とほぼ等しくする。
【００３０】
つまり考え方としては液晶層は本当は２ミクロン程度とすることがパネル設計面からは光学的には適しているが、プロセス的制約から２．５ミクロン以上としなければならず、液晶層の複屈折が大きくなりすぎ、黄色く着色してしまう。またこの黄色を防止すると光の利用効率が低下してしまう。
【００３１】
液晶層の観察者側には位相差層があり、この位相差値（複屈折値）を理想的な値からやや小さくし、液晶層の一部を位相差板と考える。そうすると液晶層が厚く、複屈折が大きくなっても位相差板の位相差値を調整することで不要な複屈折値を吸収することができ、着色を低減することができる。
【００３２】
【発明の実施の形態】
本発明における液晶配向はいわゆる平行配向と呼ばれるもので、液晶を挟持する２枚の電極基板面の配向処理方向がほぼ等しく、液晶材料がねじれることなく２枚の基板間にまっすぐ配向した状態のものである。また平行配向と呼ばれるものは平行配向と反平行配向の２種類があり、その両者を合わせてここでは平行配向と呼んでいる。つまり液晶配向を詳細に説明すると、液晶分子は配向処理をした基板面に対し数度程度立ち上がって配向している。液晶分子の面内での配向方向が同じであっても、この立ち上がりが同じ方向の場合と反対方向の場合とがあり、前者を狭義の平行配向、後者を反平行配向と呼ぶことがあり、この両者を合わせた配向状態を広義の平行配向と呼んでいる。ここではこの広義の平行配向の意味で現している。
【００３３】
また液晶配向と位相差フィルム３の遅相軸、または位相差フィルム２と３を合わせた時の遅相軸はほぼ同一であるときもっとも効果が大きい。両者のなす角が３０度以上では効果が薄くなり、良好な表示を得ることは困難であり、３０度以下のとき良好な表示を得ることができる。
【００３４】
実施例１
表１のような条件の半透過型パネルを作成し、位相差板３のみ変化させた。液晶の配向方向は９０°方向に平行（反平行）となるようにした。
【００３５】
そのときの反射特性を図３〜４に示した（なお、図３において、白丸は色度（ｘ，ｙ）のｘ成分の数値、黒丸はｙ成分の数値をそれぞれ表わす）。
【００３６】
本実施例での液晶層の複屈折は、反射部で１６３ｎｍであり、理想的なλ／４（約１４０ｎｍ）より大きく、通常では反射光が黄色く着色し、良好な表示を得ることができなかった（評価はＤ６５換算で行なった）。
【００３７】
位相差板３を変化させると、約１００ｎｍ以上の範囲で透過率は３０％を超え、また位相差値が小さいほど白色色度が良好になることが確認できた（位相差板を通常どおり１４０ｎｍとすると白色色度は（０．３５、０．３８）となり、黄色い着色により良好な表示は得られなかった）。両者の特性はトレードオフの関係にあり、１００〜１３０ｎｍの範囲では、色特性、透過率ともほぼ満足できる特性を示すことができ、さらに最適化した結果、１０５ｎｍとしたときにもっとも総合的に見たときに良好な特性を示した。同時に透過特性もすぐれており、良好な表示品位を得た。
【００３８】
本特性は上下２枚の偏光板を両方とも９０°回転した場合もほぼ同様の良好な特性となった。
【００３９】
また位相差板６をハイブリッドフィルムとすることも可能で、たとえば日石三菱社製のＮＨフィルム（商品名）とすることで視野角特性を拡大することができる。
【００４０】
さらに本実施例では位相差板をパネル上下に２枚ずつ用いて、広帯域λ／４フィルムとして用いたが、波長分散の小さな位相差板を用いた場合、上下１枚に省略することができる。それにより最適化が容易となり、コスト削減に有利である。
【００４１】
【表１】

【００４２】
実施例２
表２のような条件の半透過型パネルを作成し、位相差板３のみ変化させた。液晶の配向方向は９０°方向に平行（反平行）となるようにした。
【００４３】
そのときの反射特性を図５〜６に示した（なお、図５において、白丸は色度（ｘ，ｙ）のｘ成分の数値、黒丸はｙ成分の数値をそれぞれ表わす）。
【００４４】
本実施例での液晶層の複屈折は、反射部で１６３ｎｍであり、理想的なλ／４（約１４０ｎｍ）より大きく、通常では反射光が黄色く着色し、良好な表示を得ることができなかった（評価はＤ６５換算で行なった）。
【００４５】
位相差板３を変化させると、約１００ｎｍ以上の範囲で透過率は３０％を超え、また位相差値が小さいほど白色色度が良好になることが確認できた（位相差板を通常どおり１４０ｎｍとすると白色色度は（０．３５、０．３７）となり、黄色い着色により良好な表示は得られなかった）。両者の特性はトレードオフの関係にあり、９０〜１２５ｎｍの範囲では、色特性、透過率ともほぼ満足できる特性を示すことができ、さらに最適化した結果、１００ｎｍとしたときにもっとも総合的に見たときに良好な特性を示した。同時に透過特性もすぐれており、良好な表示品位を得た。
【００４６】
本特性は上下２枚の偏光板を両方とも９０°回転した場合もほぼ同様の良好な特性となった。
【００４７】
また位相差板６をハイブリッドフィルムとすることも可能で、たとえば日石三菱社製のＮＨフィルム（商品名）とすることで視野角特性を拡大することができる。
【００４８】
さらに本実施例では位相差板をパネル上下に２枚ずつ用いて、広帯域λ／４フィルムとして用いたが、波長分散の小さな位相差板を用いた場合、上下１枚に省略することができる。それにより最適化が容易となり、コスト削減に有利である。
【００４９】
【表２】

【００５０】
実施例３
表３のような条件の半透過型パネルを作成し、位相差板３のみ変化させた。液晶の配向方向は９０°方向に平行（反平行）となるようにした。
【００５１】
そのときの反射特性を図７〜８に示した（なお、図７において、白丸は色度（ｘ，ｙ）のｘ成分の数値、黒丸はｙ成分の数値をそれぞれ表わす）。
【００５２】
本実施例での液晶層の複屈折は、反射部で１６３ｎｍであり、理想的なλ／４（約１４０ｎｍ）より大きく、通常では反射光が黄色く着色し、良好な表示を得ることができなかった（評価はＤ６５換算で行なった）。
【００５３】
位相差板３を変化させると、約１００ｎｍ以上の範囲で透過率は３０％を超え、また位相差値が小さいほど白色色度が良好になることが確認できた（位相差板を通常どおり１４０ｎｍとすると白色色度は（０．３５、０．３９）となり、黄色い着色により良好な表示は得られなかった）。両者の特性はトレードオフの関係にあり、９０〜１２５ｎｍの範囲では、色特性、透過率ともほぼ満足できる特性を示すことができ、さらに最適化した結果、１００ｎｍとしたときにもっとも総合的に見たときに良好な特性を示した。同時に透過特性もすぐれており、良好な表示品位を得た。
【００５４】
同様条件のパネルについて位相差板３を１００ｎｍとし、その設置角度の依存性を求め、その結果を図９〜１０に示した（なお、図９において、白丸は色度（ｘ，ｙ）のｘ成分の数値、黒丸はｙ成分の数値をそれぞれ表わす）。９０°を中心に−２０°〜０°の範囲で透過率３０％を超え、５０〜１１０°（９０°を中心に−４０°〜２０°）の範囲で良好な白色色度を示した。種々の特性にはトレードオフ両者の特性はトレードオフの関係にあり、７０〜１００°の範囲では、色特性、透過率ともほぼ満足できる特性を示すことができ、さらに最適化した結果、７２°のときもっともすぐれた特性を示した。
【００５５】
本特性は上下２枚の偏光板を両方とも９０°回転した場合もほぼ同様の良好な特性となった。
【００５６】
また位相差板６をハイブリッドフィルムとすることも可能で、たとえば日石三菱社製ＮＨフィルムとすることで視野角特性を拡大することができる。
【００５７】
さらに本実施例では位相差板をパネル上下に２枚ずつ用いて、広帯域λ／４フィルムとして用いたが、波長分散の小さな位相差板を用いた場合、上下１枚に省略することができる。それにより最適化が容易となり、コスト削減に有利である。
【００５８】
【表３】

【００５９】
【発明の効果】
従来では、液晶層の複屈折値は、プロセス面の制約、液晶材料の制約より、動作原理から考えられる値より大きく設定せざるを得なかったが、本発明によれば、この差を、液晶の配向方向と遅相軸をほぼ一致させた位相差フィルムで吸収することにより、液晶層の複屈折が大きくなったことによる表示の着色を防止することができる。
【図面の簡単な説明】
【図１】本発明が適用される半透過型液晶表示装置の構造例を示す断面説明図である。
【図２】図１の各構成要素の光学的機能を模式的に示す説明図である。
【図３】本発明の液晶表示装置の実施例１の反射特性として位相差と色度との関係を示すグラフである。
【図４】本発明の液晶表示装置の実施例１の反射特性として位相差と透過率との関係を示すグラフである。
【図５】本発明の液晶表示装置の実施例２の反射特性として位相差と色度との関係を示すグラフである。
【図６】本発明の液晶表示装置の実施例２の反射特性として位相差と透過率との関係を示すグラフである。
【図７】本発明の液晶表示装置の実施例３の反射特性として位相差と色度との関係を示すグラフである。
【図８】本発明の液晶表示装置の実施例３の反射特性として位相差と透過率との関係を示すグラフである。
【図９】本発明の液晶表示装置の実施例３の反射特性として位相差板の設置角度と色度との関係を示すグラフである。
【図１０】本発明の液晶表示装置の実施例３の反射特性として位相差板の設置角度と透過率との関係を示すグラフである。
【符号の説明】
１、４偏光板
２、３、５、６位相差板
７バックライト
２１ａ、２１ｂ基板[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a liquid crystal display device. More specifically, the present invention relates to a liquid crystal display device capable of preventing display coloring due to an increase in birefringence of a liquid crystal layer.
[0002]
[Prior art]
Liquid crystal display devices can be broadly classified into two types, a reflection type and a transmission type. When both are required according to the use environment, such as a display device for a mobile phone, it is called a transflective type. A display element structure is used. An outline of the basic structure of this transflective liquid crystal display element is disclosed in a prior application or the like (see Patent Document 1).
[0003]
According to the prior application disclosed in Patent Document 1, the transflective liquid crystal display element has a region A (see FIG. 1) for performing transmissive display and a region B (see FIG. 1) for performing reflective display in the same pixel, When used for a mobile phone display element, during normal operation, the backlight installed on the back of the display element is turned on, and the display of the area A by the light emitted from the backlight transmitted through the liquid crystal display element is observed. During standby, the backlight is turned off, and the display of the area B due to external light reflected in the liquid crystal display element is observed. Accordingly, favorable display can be performed regardless of the use environment and power consumption can be reduced, so that the display device is suitable for a display element of a mobile phone or the like.
[0004]
FIG. 1 shows a structural example of a transflective liquid crystal display device disclosed in Patent Document 1. The

liquid crystal layers

22 and 23 have a structure sandwiched between the

substrates

21a and 21b, and have the circularly polarizing plate 11 on the observer side (upper side in the figure) and the circularly polarizing plate 12 on the back side (lower side in the figure). The display can be performed by changing the birefringence of the

liquid crystal layers

22 and 23 due to the electric field applied between the transparent electrode 33 on the substrate 21a, the transparent electrode 33 on the substrate 21b, and the reflecting mirror 31 having conductivity. .
[0005]
Generally, the thicknesses of the

liquid crystal layers

22 and 23 are set differently, and the difference can be adjusted by the thickness of the organic film 32 on the substrate 21b. The adjustment method and the preparation method are detailed in other prior applications and are not the object of the present application, and thus will be omitted (see Patent Document 2).
[0006]
Next, the optical function and the like of each constituent material will be described using the coordinate system shown in FIG. In FIG. 2, T ₁ and T ₂ are transmission axis directions, L ₁ , L ₂ , L ₃ , and L ₄ are slow axis directions, and R ₁ and R ₂ are rubbing axis directions.
[0007]
In FIG. 2, the rubbing directions of the

substrates

21a and 21b are the same, and the liquid crystal is in a so-called parallel alignment (including anti-parallel alignment). When an electric field is applied to the electrodes on both substrate surfaces, when a liquid crystal material having a positive dielectric anisotropy is used, the liquid crystal molecules gradually move from the substrate surface from an alignment state substantially parallel to the substrate surface when no electric field is applied. The orientation changes to a rising orientation, and the birefringence decreases accordingly. In the most basic configuration, the birefringence when no electric field is applied is λ / 4 with respect to the wavelength λ of light in the liquid crystal layer 22 for reflective display and λ / 2 for the liquid crystal layer 23 for transmissive display. Adjust the thickness of the liquid crystal material and each liquid crystal layer. When an electric field is applied and the liquid crystal molecules become almost perpendicular to the substrate surface, the birefringence becomes almost 0. Therefore, the change in the birefringence due to the voltage application is λ / 4 at the reflection part (in the reflection part, incident light reciprocates. Λ / 4 × 2 = λ / 2), and λ / 2 in the transmission part. In practice, the birefringence when a voltage is applied does not become completely zero, so that the birefringence of the

liquid crystal layers

22 and 23 when no voltage is applied is often set to be slightly larger.
[0008]
The two

phase difference plates

2 and 3 are arranged so as to exhibit a characteristic of λ / 4 over a wide wavelength range. Generally, the phase difference plate 2 is approximately λ / 2 and the phase difference plate 3 Uses a uniaxially stretched film having a property of λ / 4. However, in recent years, a film exhibiting a characteristic of λ / 4 in a wide wavelength range even when used alone has been developed. In that case, the retardation plate 2 can be omitted.
[0009]
The

retardation plates

5 and 6 are also arranged so as to be λ / 4 in the same manner as 2 and 3, and the retardation plate 5 can be omitted according to the characteristics.
[0010]
From the above, the typical structure and the function of each member described in the prior art are summarized as follows.
Polarizing plate 1: Incoming and outgoing light is converted into linearly polarized light. Phase difference plates 2, 3: Total λ / 4
Liquid crystal layer 22: birefringence λ / 4 (λ / 4 × 2 = λ / 2 due to reciprocation by reflection), almost 0 when voltage is applied
Liquid crystal layer 23: birefringence λ / 2, almost 0 when voltage is applied
Phase difference plates 5 and 6: combined λ / 4
Polarizing plate 4: Converts light from backlight to linearly polarized light
At this time, the display mechanism is as follows.
[0012]
<< Reflection display >>
(White display: no voltage applied)
The

phase difference plates

2 and 3 contribute λ / 2 at the time of incidence and λ / 4 at the time of reflection as a total λ / 2.
[0013]
The liquid crystal layer contributes as a round trip λ / 2. Totals λ.
[0014]
Accordingly, the linearly polarized light that has passed through the polarizing plate 1 is shifted in phase by one period and returns to the polarizing plate 1 in the original polarization state, so that the linearly polarized light can pass through the polarizing plate 1 and display white.
[0015]
(Black display: Birefringence of liquid crystal layer by voltage application = almost 0)
As described above, the phase difference plate contributes as λ / 2 in a reciprocating manner.
[0016]
The liquid crystal layer is 0. The total is λ / 2.
[0017]
The linearly polarized light that has passed through the polarizing plate 1 has a phase shift of 周期 period, and thus returns to the polarizing plate 1 after being rotated 90 ° from the original polarization state. .
[0018]
<< Transparent display >>
(White display: no voltage applied)
Λ / 4 × 2 = λ / 2 for the

phase difference plates

2, 3, 5 and 6.
[0019]
The liquid crystal layer becomes λ / 2. Totals λ.
[0020]
Since the linearly polarized light transmitted through the polarizing plate 4 reaches the polarizing plate 1 in the same polarization state, a white display is obtained if the transmission axes of the polarizing plates 1 and 4 are almost matched.
[0021]
(Black display: Birefringence of liquid crystal layer by voltage application = almost 0)
The retardation plate has a total of λ / 2.
[0022]
The liquid crystal layer is 0. The total is λ / 2.
[0023]
The linearly polarized light that has passed through the polarizing plate 4 reaches the polarizing plate 1 after being rotated by 90 °. Therefore, if the transmission axes of the polarizing plates 1 and 4 are almost aligned, the linearly polarized light cannot be transmitted and black display is performed.
[0024]
[Patent Document 1]
Japanese Patent Application Laid-Open No. 2000-187220 [Patent Document 2]
JP-A-10-186359
[Problems to be solved by the invention]
Currently available liquid crystal materials have a refractive index anisotropy (Δn) of 0.065 to 0.1 with respect to a wavelength of 550 nm, and a birefringence (Δnd: d is a thickness of the liquid crystal layer) at a reflection portion using these liquid crystals. In order to make λ / 4), the panel gap must be 2.1 microns or less, but 2.5 microns is the lower limit for stable production in the current panel manufacturing process. Therefore, the birefringence of the liquid crystal layer in the reflective portion becomes large, and first, coloring becomes large as a first problem. Generally, in such a case, there is a problem that yellow coloring is remarkable and display quality is remarkably reduced.
[0026]
Further, in the liquid crystal display device of the present application, the liquid crystal alignment of the liquid crystal layer is described only for the parallel alignment. However, conventionally, the liquid crystal alignment is twisted (the alignment direction of the liquid crystal is different between the upper and lower substrates, and the liquid crystal is Many transflective liquid crystal display elements (in which molecules are twisted) have been developed. When this twist orientation is used, black and white display can be performed for the reflective portion in the same manner as the mechanism described above, but for the transmissive portion, elliptically polarized light is reached when the light reaches the upper polarizing plate during white display. Since only one polarized light component can be transmitted, there is a problem that the light utilization efficiency is halved compared to the case of the parallel orientation of the present invention, and there is a history that the use of the parallel orientation has made a great improvement.
[0027]
Adjustment of the polarizing plate and retardation plate on the viewer side of the liquid crystal layer to solve the coloring problem described above often resulted in the transmission part, which was obtained by adopting the parallel alignment in many cases. High transmittance will be sacrificed.
[0028]
In view of the above, the present invention proposes a panel configuration that reduces coloring of a reflective portion while sufficiently maintaining a high transmittance using parallel alignment.
[0029]
[Means for Solving the Problems]
The slow axis of the retardation plate 3 or the retardation layer formed by combining the

retardation plates

2 and 3 on the observer side of the liquid crystal display element is made substantially coincident with the orientation direction of the liquid crystal, and the birefringence value is changed to the wavelength of light. λ is smaller than λ / 4. The degree to which the birefringence value is smaller than λ / 4 is substantially equal to the amount of the birefringence value of the liquid crystal layer of the reflection portion exceeding λ / 4.
[0030]
In other words, it is optically suitable from the viewpoint of panel design that the liquid crystal layer is actually about 2 microns, but it must be 2.5 microns or more due to process restrictions. It becomes too large and is colored yellow. Further, if this yellow color is prevented, the light use efficiency is reduced.
[0031]
There is a retardation layer on the viewer side of the liquid crystal layer, and this retardation value (birefringence value) is made slightly smaller than an ideal value, and a part of the liquid crystal layer is considered as a retardation plate. Then, even if the liquid crystal layer is thick and the birefringence becomes large, unnecessary birefringence values can be absorbed by adjusting the retardation value of the retardation plate, and coloring can be reduced.
[0032]
BEST MODE FOR CARRYING OUT THE INVENTION
The liquid crystal alignment in the present invention is what is called parallel alignment, in which the alignment directions of the two electrode substrate surfaces sandwiching the liquid crystal are substantially equal, and the liquid crystal material is aligned straight between the two substrates without twisting. It is. There are two types of so-called parallel orientations, a parallel orientation and an anti-parallel orientation, and both are collectively referred to herein as a parallel orientation. In other words, the liquid crystal alignment will be described in detail. The liquid crystal molecules are aligned by rising about several degrees with respect to the alignment-treated substrate surface. Even if the orientation direction in the plane of the liquid crystal molecules is the same, there are cases where this rise is in the same direction and in the opposite direction, the former may be referred to as parallel orientation in a narrow sense, and the latter may be referred to as anti-parallel orientation, The orientation state combining these two is called a parallel orientation in a broad sense. Here, this is expressed in the broad sense of parallel orientation.
[0033]
The effect is greatest when the liquid crystal alignment and the slow axis of the retardation film 3 or the slow axis when the

retardation films

2 and 3 are combined are substantially the same. If the angle between them is 30 degrees or more, the effect is weak, and it is difficult to obtain a good display. If the angle is 30 degrees or less, a good display can be obtained.
[0034]
Example 1
A transflective panel under the conditions shown in Table 1 was prepared, and only the retardation plate 3 was changed. The alignment direction of the liquid crystal was parallel (anti-parallel) to the 90 ° direction.
[0035]
The reflection characteristics at that time are shown in FIGS. 3 and 4 (in FIG. 3, white circles represent the numerical value of the x component of chromaticity (x, y), and black circles represent the numerical value of the y component, respectively).
[0036]
The birefringence of the liquid crystal layer in the present embodiment is 163 nm at the reflection part, which is larger than the ideal λ / 4 (about 140 nm). Normally, the reflected light is colored yellow, and good display cannot be obtained. (Evaluation was performed in D65 conversion).
[0037]
When the retardation plate 3 was changed, it was confirmed that the transmittance exceeded 30% in the range of about 100 nm or more, and that the smaller the retardation value, the better the white chromaticity was. Then, the white chromaticity was (0.35, 0.38), and good display was not obtained due to yellow coloring.) There is a trade-off between the two characteristics. In the range of 100 to 130 nm, both color characteristics and transmittance can be almost satisfied, and as a result of further optimization, the best overall performance is obtained at 105 nm. Exhibited good characteristics. At the same time, the transmission characteristics were excellent, and good display quality was obtained.
[0038]
The characteristics were almost the same when the upper and lower polarizing plates were both rotated by 90 °.
[0039]
Also, the retardation plate 6 can be a hybrid film. For example, the viewing angle characteristic can be expanded by using an NH film (trade name) manufactured by Mitsubishi Nisseki Co., Ltd.
[0040]
Further, in the present embodiment, two retardation plates are used at the top and bottom of the panel and used as a broadband λ / 4 film. However, when a retardation plate with small wavelength dispersion is used, it can be omitted for one upper and lower plate. This facilitates optimization and is advantageous for cost reduction.
[0041]
[Table 1]

[0042]
Example 2
A transflective panel under the conditions shown in Table 2 was prepared, and only the retarder 3 was changed. The alignment direction of the liquid crystal was parallel (anti-parallel) to the 90 ° direction.
[0043]
The reflection characteristics at that time are shown in FIGS. 5 and 6 (in FIG. 5, white circles represent the numerical value of the x component of chromaticity (x, y), and black circles represent the numerical value of the y component).
[0044]
The birefringence of the liquid crystal layer in the present embodiment is 163 nm at the reflection part, which is larger than the ideal λ / 4 (about 140 nm). Normally, the reflected light is colored yellow, and good display cannot be obtained. (Evaluation was performed in D65 conversion).
[0045]
When the retardation plate 3 was changed, it was confirmed that the transmittance exceeded 30% in the range of about 100 nm or more, and that the smaller the retardation value, the better the white chromaticity was. , The white chromaticity was (0.35, 0.37), and good display was not obtained due to yellow coloring). There is a trade-off between the two characteristics. In the range of 90 to 125 nm, both the color characteristics and the transmittance can be almost satisfied. Exhibited good characteristics. At the same time, the transmission characteristics were excellent, and good display quality was obtained.
[0046]
The characteristics were almost the same when the upper and lower polarizing plates were both rotated by 90 °.
[0047]
Also, the retardation plate 6 can be a hybrid film. For example, the viewing angle characteristic can be expanded by using an NH film (trade name) manufactured by Mitsubishi Nisseki Co., Ltd.
[0048]
Further, in the present embodiment, two retardation plates are used at the top and bottom of the panel and used as a broadband λ / 4 film. However, when a retardation plate with small wavelength dispersion is used, it can be omitted for one upper and lower plate. This facilitates optimization and is advantageous for cost reduction.
[0049]
[Table 2]

[0050]
Example 3
A transflective panel under the conditions shown in Table 3 was prepared, and only the retarder 3 was changed. The alignment direction of the liquid crystal was parallel (anti-parallel) to the 90 ° direction.
[0051]
The reflection characteristics at that time are shown in FIGS. 7 and 8 (in FIG. 7, white circles represent the numerical value of the x component of chromaticity (x, y), and black circles represent the numerical value of the y component).
[0052]
The birefringence of the liquid crystal layer in the present embodiment is 163 nm at the reflection part, which is larger than the ideal λ / 4 (about 140 nm). Normally, the reflected light is colored yellow, and good display cannot be obtained. (Evaluation was performed in D65 conversion).
[0053]
When the retardation plate 3 was changed, it was confirmed that the transmittance exceeded 30% in the range of about 100 nm or more, and that the smaller the retardation value, the better the white chromaticity was. , The white chromaticity was (0.35, 0.39), and good display was not obtained due to yellow coloring.) There is a trade-off between the two characteristics. In the range of 90 to 125 nm, both the color characteristics and the transmittance can be almost satisfied. Exhibited good characteristics. At the same time, the transmission characteristics were excellent, and good display quality was obtained.
[0054]
With respect to the panel under the same conditions, the phase difference plate 3 was set to 100 nm, and the dependence of the installation angle was obtained. The results are shown in FIGS. 9 to 10 (in FIG. 9, white circles indicate x of chromaticity (x, y)). The numerical value of the component and the black circle represent the numerical value of the y component, respectively. The transmittance exceeded 30% in the range of -20 ° to 0 ° around 90 °, and showed good white chromaticity in the range of 50 to 110 ° (-40 ° to 20 ° around 90 °). Various characteristics have a trade-off relationship between the two characteristics. Within the range of 70 to 100 °, both color characteristics and transmittance can be almost satisfied. In the case of, the most excellent characteristics were shown.
[0055]
The characteristics were almost the same when the upper and lower polarizing plates were both rotated by 90 °.
[0056]
Also, the retardation plate 6 can be a hybrid film. For example, by using an NH film manufactured by Nisseki Mitsubishi Corporation, the viewing angle characteristics can be expanded.
[0057]
Further, in the present embodiment, two retardation plates are used at the top and bottom of the panel and used as a broadband λ / 4 film. However, when a retardation plate with small wavelength dispersion is used, it can be omitted for one upper and lower plate. This facilitates optimization and is advantageous for cost reduction.
[0058]
[Table 3]

[0059]
【The invention's effect】
In the past, the birefringence value of the liquid crystal layer had to be set to be larger than the value conceivable from the operating principle due to the limitations of the process surface and the limitation of the liquid crystal material. Absorption by a retardation film whose alignment direction and the slow axis are almost coincident with each other can prevent display coloring due to an increase in birefringence of the liquid crystal layer.
[Brief description of the drawings]
FIG. 1 is a cross-sectional explanatory view showing a structural example of a transflective liquid crystal display device to which the present invention is applied.
FIG. 2 is an explanatory diagram schematically showing an optical function of each component of FIG. 1;
FIG. 3 is a graph illustrating a relationship between a phase difference and chromaticity as a reflection characteristic of the liquid crystal display device according to the first embodiment of the present invention.
FIG. 4 is a graph showing a relationship between a phase difference and a transmittance as a reflection characteristic of the liquid crystal display device according to the first embodiment of the present invention.
FIG. 5 is a graph showing a relationship between a phase difference and chromaticity as a reflection characteristic of the liquid crystal display device according to the second embodiment of the present invention.
FIG. 6 is a graph showing a relationship between a phase difference and a transmittance as a reflection characteristic of the liquid crystal display device according to the second embodiment of the present invention.
FIG. 7 is a graph showing the relationship between the phase difference and the chromaticity as the reflection characteristic of the liquid crystal display device according to the third embodiment of the present invention.
FIG. 8 is a graph showing a relationship between a phase difference and a transmittance as a reflection characteristic of the liquid crystal display device according to the third embodiment of the present invention.
FIG. 9 is a graph showing a relationship between an installation angle of a retardation plate and chromaticity as a reflection characteristic of a liquid crystal display device according to a third embodiment of the present invention.
FIG. 10 is a graph showing the relationship between the installation angle of the retardation plate and the transmittance as the reflection characteristic of the liquid crystal display device of Example 3 of the present invention.
[Explanation of symbols]
1, 4

polarizing plate

2, 3, 5, 6 retardation plate 7

backlight

21a, 21b substrate

Claims

A transflective liquid crystal display device in which the liquid crystal alignment is parallel alignment, wherein a polarizing plate is arranged on the panel surface on the observer side of the liquid crystal display device from the observer side to be approximately λ / 2 with respect to the wavelength λ of light. In a transflective liquid crystal display device having a structure that becomes a retardation film, a retardation film having a substantially λ / 4, and a glass substrate of a panel, a retardation compensation layer formed by laminating the two retardation films is formed. A liquid crystal display device in which the phase axis substantially coincides with the orientation direction of the liquid crystal and the birefringence value is set smaller than λ / 4.

A transflective liquid crystal display device in which the liquid crystal alignment is parallel alignment, wherein a polarizing plate is arranged on the panel surface on the observer side of the liquid crystal display device from the observer side to be approximately λ / 2 with respect to the wavelength λ of light. In a transflective liquid crystal display device having a structure in which a retardation film, a retardation film having a wavelength of approximately λ / 4, and a glass substrate of a panel, the slow axis of the retardation film having a wavelength of approximately λ / 4 on the panel has a liquid crystal orientation. A liquid crystal display device substantially coincident with the direction and having a birefringence value set to be smaller than λ / 4.

A transflective liquid crystal display device in which the liquid crystal alignment is parallel alignment, wherein a polarizing plate is disposed on the panel surface on the observer side of the liquid crystal display device from the observer side so that the wavelength becomes approximately １／ λ with respect to the wavelength λ of light. In a transflective liquid crystal display device having a structure that becomes a phase difference film and a glass substrate of a panel, the slow axis of the phase difference film, which is approximately 1 / 4λ on the panel, almost coincides with the orientation direction of the liquid crystal, and the birefringence value is increased. A liquid crystal display device characterized by being set to be smaller than ４λ.

4. The liquid crystal display device according to claim 1, wherein the liquid crystal alignment substantially coincides with the slow axis of the retardation film in a range of ± 30 degrees.

4. The liquid crystal display device according to claim 1, wherein a birefringence value of the retardation film composed of one or two sheets and a birefringence value of a liquid crystal layer in a reflective display portion are approximately λ / 2. .

Of the two retardation films, the birefringence value of the retardation film in contact with the panel and having a birefringence of approximately λ / 4 and the birefringence value of the liquid crystal layer of the reflective display portion are approximately λ / 2. The liquid crystal display device according to claim 1, 2 or 3.

The sum of the birefringence value of the retardation film composed of one or two sheets and the birefringence value of the liquid crystal layer in the reflective display portion is in a range of approximately 0.7 × λ / 2 to 1.3 × λ / 2. The liquid crystal display device according to claim 5, wherein

Of the two retardation films, the birefringence value of the retardation film having a birefringence of approximately λ / 4, which is in contact with the panel, and the birefringence value of the liquid crystal layer in the reflective display portion are approximately 0.1. 7. The liquid crystal display device according to claim 6, wherein the range is 7 × λ / 2 to 1.3 × λ / 2.